diff --git a/bin/loader.cpp b/bin/loader.cpp
index 6f066e3..c28c9ba 100644
--- a/bin/loader.cpp
+++ b/bin/loader.cpp
@@ -454,11 +454,9 @@ std::string find_exe(const std::string &name)
 	// if name is a path, then it doesn't exist.
 	if (name.find('/') != name.npos) return std::string();
 
+	std::string path = MPW::RootDir();
+	if (path.empty()) return path;
 
-	const char *mpw = getenv("MPW");
-	if (!mpw || !*mpw) return std::string();
-
-	std::string path(mpw);
 
 	if (path.back() != '/') path.push_back('/');
 	path.append("Tools/");
@@ -468,47 +466,6 @@ std::string find_exe(const std::string &name)
 
 	return std::string();
 
-
-
-#if 0
-	std::string subpath;
-	// check in $MPW/name.
-	const char *cpath = getenv("mpw_path");
-	if (!cpath) return std::string();
-
-	path = cpath; 
-	// split on :
-
-	if (path.empty()) return std::string();
-
-	int start = 0, end = 0;
-
-	while ((end = path.find(':', start)) != path.npos)
-	{
-		subpath = path.substr(start, end - start);
-
-		if (subpath.length())
-		{
-			subpath.push_back('/');
-			subpath.append(name);
-
-			if (file_exists(subpath)) return subpath;			
-		}
-
-		start = end + 1;
-	}
-
-	subpath = path.substr(start);
-	if (subpath.length())
-	{
-		subpath.push_back('/');
-		subpath.append(name);
-
-		if (file_exists(subpath)) return subpath;
-	}
-
-	return std::string();
-#endif
 }
 
 
diff --git a/mpw/mpw.cpp b/mpw/mpw.cpp
index 74bc03e..c66b37a 100644
--- a/mpw/mpw.cpp
+++ b/mpw/mpw.cpp
@@ -14,6 +14,8 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <libgen.h>
+#include <sys/stat.h>
+#include <pwd.h>
 
 #include <cpu/defs.h>
 #include <cpu/fmem.h>
@@ -91,6 +93,100 @@ namespace MPW
 
 	}
 
+	static bool isdir(const std::string &path)
+	{
+		struct stat st;
+		if (stat(path.c_str(), &st) < 0) return false;
+		return S_ISDIR(st.st_mode);
+	}
+
+	const std::string RootDir()
+	{
+		static bool initialized = false;
+		static std::string path;
+
+		static const std::string paths[] = {
+			"/usr/local/share/mpw",
+			"/usr/share/mpw",
+		};
+
+		char *cp;
+		struct passwd *pw;
+
+		if (initialized) return path;
+
+		initialized = true;
+
+		// check $MPW, $HOME/mpw, /usr/local/share/mpw/, /usr/share/mpw
+		// for a directory.
+
+		cp = getenv("MPW");
+		if (cp && *cp)
+		{
+			std::string s(cp);
+			if (isdir(s))
+			{
+				path = std::move(s);
+				return path;
+			}
+		}
+
+		// home/mpw
+		pw = getpwuid(getuid());
+		if (pw && pw->pw_dir && pw->pw_dir[0])
+		{
+			std::string s(pw->pw_dir);
+			if (s.back() != '/') s.push_back('/');
+			s.append("mpw");
+
+			if (isdir(s))
+			{
+				path = std::move(s);
+				return path;
+			}
+		}
+#if 0
+		// thread-safe
+		{
+			int size;
+
+			size = sysconf(_SC_GETPW_R_SIZE_MAX);
+			if (size >= 0)
+			{
+				struct passwd pwd, *result = nullptr;
+				char *buffer = alloca(size);
+
+				if (getpwuid_r(getuid(), &pwd, buffer, size, &result) == 0 && result)
+				{
+					std::string s(pwd.pw_dir);
+					if (s.back() != '/') s.push_back('/');
+					s.append("mpw");					
+					if (isdir(s))
+					{
+						path = std::move(s);
+						return path;
+					}
+				}
+			}
+		}
+#endif
+		for (auto &iter : paths)
+		{
+			if (isdir(iter))
+			{
+				path = iter;
+				return path;
+			}
+
+		}
+
+
+
+		return path; // unknown.
+	}
+
+
+
 	uint16_t Init(int argc, char **argv)
 	{
 		/*
@@ -194,20 +290,18 @@ namespace MPW
 		{
 			std::unordered_map<std::string, std::string> env;
 
-			const char *mpw = getenv("MPW");
-			if (mpw && *mpw)
+			std::string m(RootDir());
+			if (!m.empty())
 			{
-				std::string m(mpw);
-				m = ToolBox::UnixToMac(m);
-				if (m.back() != ':') m.push_back(':');
+				std::string mm = ToolBox::UnixToMac(m);
+				if (mm.back() != ':') mm.push_back(':');
 
-				env.emplace(std::string("MPW"), m);
+				env.emplace(std::string("MPW"), mm);
 			}
 			env.emplace(std::string("Command"), command);
 
-			if (mpw && *mpw)
+			if (!m.empty())
 			{
-				std::string m(mpw);
 
 				void LoadEnvironment(std::string &envfile, std::unordered_map<std::string, std::string> &env);
 
diff --git a/mpw/mpw.h b/mpw/mpw.h
index ef55c43..5a56611 100644
--- a/mpw/mpw.h
+++ b/mpw/mpw.h
@@ -2,6 +2,7 @@
 #define __mpw_mpw_h__
 
 #include <cstdint>
+#include <string>
 
 namespace MPW {
 
@@ -91,6 +92,7 @@ namespace MPW {
 	};
 
 
+	const std::string RootDir();
 
 	// should add argc/argv/envp...
 	uint16_t Init(int argc, char **argv);